Old-fashioned love story ... Janet Gaynor and George O'Brien in Sunrise: A Song of Two Humans (1927). Photograph: Ronald Grant Archive

The twist is supposed to arrive at the end of the movie, but Sunrise: A Song of Two Humans pulls the rug from under our feet just a third of the way in. We're suddenly offered a chance of happiness, as the film diverts down an unexpected path. It's a disconcerting but ultimately liberating jolt – as if Humphrey Bogart had stopped following Lauren Bacall around in The Big Sleep and taken that nice librarian out for dinner instead.

Sunrise begins, as so many great films do, with the promise of sex and the threat of violence. Two clandestine lovers meet in the moonlight and dream of committing the perfect murder. But is Man (George O'Brien) really prepared to drown his sweet young wife (Janet Gaynor), sell his farm and move to a more exciting life in the city with his vamp girlfriend?

Margaret Livingston, as Woman from the City dripping poison into our hero's ear, is certainly seductive – all black satin, cigarettes and bobbed hair. When she dances she conjures a vision of bright lights and glamour, and the promise of a better, more modern life. But this witchcraft is to be feared: she's a proto-femme fatale. When Man is pictured at home with Wife, Woman is superimposed on his shoulders, preying on him, crushing him. He can't stop thinking about her and her plan, so he invites his wife to take a boat ride with him, and to leave the baby at home.

George O'Brien and Margaret Livingstone in Sunrise: A Song of Two Humans (1927). Photograph: Ronald Grant Archive

Sunrise was made in 1927, way before the rise of film noir in the 1940s, but you'd be forgiven for thinking the film comes from the later decade. Sunrise isn't a crime drama, it isn't even a classic romance: it's a film about the rekindling of true love. The twist (spoiler alert – I can't resist telling you) is that the hero doesn't kill his wife. When it comes to the crucial moment he can't quite summon up … the nerve? He's no villain, not really. He falters, she escapes, he catches up to her – but they're in a public place, on a tram to the city, and neither of them can discuss what just happened out on the lake. So they go to the city together instead.

It's far more difficult to tell you what happens next, because it looks so ridiculous written down. Their day trip turns into a symbolic remarriage: there's tears, dancing and a piglet running loose in a nightclub. At the end, there's danger, then tragedy strikes … and by that point I'm usually whimpering quietly on the sofa.

Jant Gaynor and George O'Brien in Sunrise: A Song of Two Humans (1927). Photograph: Ronald Grant Archive

It's worth saying that the film isn't modern or cool in the slightest, and I don't care. The two lead characters with their daft, bumpkinish ways are old-fashioned people from an old-fashioned place, and they're completely out of their depth in the city. The humour is gentle rather than wisecracking. It's sentimental – which is a dirty word these days, but cynicism doesn't make anyone happy. What Sunrise wants to achieve is universality, which is the reason for the portentous subtitle, and why none of the characters has a name. The first intertitle reads: "This song of the Man and his Wife is of no place and every place; you might hear it anywhere, at any time."

Intertitle? If you hadn't guessed already, Sunrise is a silent film. And to be honest, though Hollywood would continue to make them for a few years more, silent films were becoming passé when it was released. It was the same year as The Jazz Singer, which I see as a far inferior movie. The US release of Sunrise was saddled with a Movietone soundtrack – music mostly, some animal noises and car horns, but no dialogue – arguably, 21st-century viewers will find the sound the most dated thing about the film.

George O'Brien in Sunrise: A Song of Two Humans (1927), directed by FW Murnau. Photograph: Ronald Grant Archive

Producer William Fox had given the newly imported German director FW Murnau free rein for this film, and the result was beautiful sets lit from all angles (making it easier for the heavy hand-cranked cameras to be pushed around). Murnau's films are gorgeous, and Sunrise is no exception. Its luscious black-and-white photography and sweeping camera moves haven't aged a bit. The best way to watch Sunrise is with no soundtrack, only live music, as was done on its release in Europe.

This film is precious, not least because it belongs to a lost time – it's one of the silent era's final hurrahs. At its close you will have forgotten – unless you have a heart of stone – the flashy allure of Woman from the City and fallen for Man, Wife and their rustic charms. Likewise, you couldn't watch this film and wish it were made in colour, with talking bits. It's perfect as it is, a monochrome fairytale.